Early into her set at the Walmart AMP, Lambert welcomed Monroe and Presley to the stage to sing "Hell on Heels" and "Takin' Pills," both from 2011's Hell on Heels album. Readers can press play on the video above to watch a snippet of their performance of "Hell on Heels."

The Annies have been known to show up at Lambert's shows: In October of 2015, they performed together at an Augusta, Ga., stop on Lambert's Roadside Bars and Pink Guitars Tour; however, they haven't released any new music since their sophomore disc, Annie Up, in 2013. That June, the trio abruptly canceled all of their upcoming concerts, and rumors of a breakup began swirling, but all three artists have denied the rumors of tension among them.

“We’ve been missing each other a lot,” Monroe said in November of 2015, adding that a reunion is "definitely brewing."

“We have a lot of song ideas going," she said at the time. "I feel like it’s soon.”

Still, Monroe explains, they “never want to force it.”

“You know, Pistol Annies started out that it was just organic: Me and Miranda thought of it on a couch; she had never met Angaleena, and we called her and got started,” Monroe recalls. “… If we’re too busy, then don’t force it. There’ll be a time when things let up a little bit, then we’ll make more music.”

In the years since Pistol Annies' last album, Lambert, Monroe and Presley have all released solo projects. Lambert is set to release a brand-new single, "Vice," on Monday (July 18).